Strengthening the alloys with elastic softening in shear modulus C′

A multifunctional titanium based alloy, Gum Metal, has very low C′ (=(C₁₁ - C₁₂)/2), which is similar to shape memory alloys (SMAs). The Peierls stress would be relatively low in such low C′ alloys, however, it has been reported that dislocation activity in Gum Metal is suppressed up to its ideal shear strength. Recently, a Fe-Ni-Co-Ti alloy with very fine grain size processed by severe plastic deformation (SPD) has also been reported to have similar mechanical properties to Gum Metal. In the present paper, some recent discussions on elastic and plastic behaviors in these alloys were summarized. The reduced C′ enhances elastic anisotropy and significantly decreases the ideal shear strength. It also results in significant core spreading of screw dislocations which can raise the critical shear stress for dislocation glide, if such cores interact with other neighboring ones, solute elements or solute clusters. Mechanical responses to loading were also discussed in Gum Metal and the SPDed Fe-Ni-Co-Ti alloy using stress-temperature diagram, which has been often used to explain the behavior of SMAs.